Molecular detection of AmpC-beta lactamase CITM gene in gram-negative bacterial isolates obtained from clinical specimens in a tertiary hospital in Nigeria.

In most developing countries, the β-lactam antibiotics are still the most predominantly prescribed antibiotics to treat bacterial infections. Resistance to third-generation cephalosporins is typical of multidrug resistance (MDRs), being mainly due to the production of AmpC-type β-lactamases. The aim of the study was to detect blaCITM gene in Gram-negative bacterial isolates obtained from clinical specimens in a tertiary hospital. A total of 220 Gram-negative bacterial isolates obtained from clinical specimens were involved in the study. The primary screening of the AmpC enzyme-producing strains was conducted by the Kirby-Bauer disk diffusion method. Isolates that yielded a zone diameter ≤18 mm (screen positive) to cefoxitin sensitivity disc were further subjected to confirmatory tests using the AmpC disc test technique. Genomic DNA was extracted using Quick-DNATM Fungal/Bacterial Miniprep Kit; Zymo Research). Conventional Polymerase Chain Reaction (PCR) analysis was carried out in order to detect the presence of blaCITM. Out of 220 isolates, 45 (20.5%) were found to be resistant to cefoxitin (Screening test for AmpC β-lactamase) of which 10 (4.5%) were positive for AmpC β-lactamase (confirmatory positive by AmpC Disk Test). However, polymerase chain reaction (PCR) analysis revealed that none of the isolates harboured the blaCITM gene. The results from this study implied that not all cefoxitin resistant isolates are AmpC β-lactamase producers. The absence of blaCITM gene may be as a result of other enzymatic mechanism such as extended spectrum beta lactamases (ESBLs) and metallo beta-lactamase (MBL) or because of the non-enzymatic mechanism such as porin channel mutation.